In raw material fluid supply apparatuses and the like of semiconductor manufacturing equipment, process gas having a stable concentration is required to be supplied to a processing device for improving quality of a semiconductor product.
Thus, in the conventional raw material fluid supply apparatuses of this kind such as a bubbling-type raw material fluid supply apparatus as shown in FIG. 7, an infrared absorption type concentration meter 22 is provided near a vaporized raw material outlet of a temperature controlled raw material tank 21, and process gas 24, e.g., process gas including vaporized organic metal raw material such as trimethylgallium (TMGa), having a predetermined raw material concentration is supplied to a reactor 23, while adjusting a temperature of the raw material tank 21, a flow rate of career gas CG, a vapor pressure Po in tank and the like based on concentration detection signals output from the concentration meter 22.In FIG. 7, a reference sign 25 designates a thermal mass flow controller of the career gas, a reference sign 26 designates a pressure regulator of the tank pressure, a reference sign 33 designates a supply line of the career gas, a reference sign 34 designates a discharge line of exhaust gas, and a reference sign G designates raw material gas. Here, not only liquid raw material but sublimable solid raw material may be used as a source of the raw material gas included in the process gas 24.
As the infrared absorption type concentration meter 22, concentration meters with various configurations are practically used though, the inline concentration meter 22 includes a sample cell 30a through which the raw material gas G flows, a reference cell 30b through which reference gas C flows, a light source 28 that emits infrared light into the respective cells, a light quantity detector 29 for the lights that have passed through the respective cells, and a computing device (not shown) for computing a concentration of the raw material based on absorbances found from detection signals output from the detector 29 as shown in FIG. 8. Here, a reference sign A designates a preamplifier, a reference sign S designates the semiconductor manufacturing equipment, and a reference sign SC designates a light transmitting window. The light source 28 moves upwards and downwards integrally with the light receiver 29 to emit light into the sample cell 30a as well as the reference cell 30b. (Japanese Laid-Open Patent Publication No. 2000-206045)
Then in the concentration meter 22 shown in FIG. 8, the absorbance of the gas in the sample cell 30a is measured and the concentration of the gas is computed by applying the Beer-Lambert law and others to the measured absorbance.
At this point, appropriate corrections for measurements including a zero point adjustment are made by sliding upwards the light source 28 and the light receiver 29 integrally and detecting the absorbance of the reference cell 30b 
However, the infrared absorption type concentration meter 22 has problems such as (I) instability of the detector 29 due to rather large fluctuations of the light source 28, (II) low responsiveness due to an absorbance averaging process that leads to relatively poor concentration detection sensitivity, and (III) increase in size as well as production cost of the detector 29 that requires the cells 30a and 30b, both of which have relatively long light paths.
Furthermore, in order to continuously conduct the stable gas concentration measurement for a long term, transparency of the light transmitting window SC needs to last for a long time, and in case the transparency changes with time, the stable gas concentration measurement becomes difficult.
For improving measurement speeds and S/N ratios or the like of infrared absorption type spectrophotometers, Fourier transform infrared (FT-IR) spectrophotometers have been developed and utilized, where non-dispersive optical systems with interferometers are used instead of dispersion type optical systems with diffraction gratings and/or slits to detect all wavelengths simultaneously and calculate a luminous intensity of each wavelength component by applying Fourier transformation to the detected values.
However, even in the concentration meter with the FT-IR spectrophotometers, the problems of the poor measurement precision and low reproducibility due to fluctuations of the light source are left unsolved because wavelength regions for measurement are basically equal to an infrared region.
Frequency ranges for measurement may be expanded to from far infrared to visible light by changing light sources, beam splitters, detectors, light transmitting windows and the like, though it is actually difficult to implement the spectrum expansion due to troubles for exchanges of the components and/or various problems due to the infrared system.
On the other hand, gas concentration meters using ultraviolet light have been developed for solving the problems including poor responsiveness and/or low measurement precision in the infrared absorption method.
FIG. 9 illustrates a configuration outline of the device, and a light source 28 includes a light source unit 28a having an ultraviolet light lamp that emits ultraviolet light with wavelengths of 200 to 400 nm (for example, a deuterium lamp and Hg—Xe lamp) and a spectroscope 28b. 
In other words, as shown in FIG. 9, the gas concentration meter includes a sample cell 30a through which raw material gas G flows, a reference cell 30b through which reference gas C flows, the light source unit 28a and the spectroscope 28b that emit ultraviolet light into the respective cells, a light quantity detector 29 for the lights that have passed through the respective cells, and a computing device (not shown) for calculating a concentration of the raw material based on absorbances found from detection signals which are output from 29a of the detector. Here, a reference sign 31 designates a gas purification device, a reference sign 32 designates a pump, a reference sign 35 designates an exhaust gas treatment device, a reference sign M designates a mirror, a reference sign MP designates a diffraction grating, a reference sign ML designates a slit, a reference sign MS designates a sector mirror, and a reference sign MG designates a grating mirror. (Japanese Laid-Open Patent Publication No. 2005-241249)
In the ultraviolet light gas concentration meter, even though the absorbance of the reference cell 30b is detected with the double-beam type spectroscope 28b to conduct appropriate corrections of measurement values including a zero point adjustment, the problems of the large fluctuations of the light source 28 and relatively poor responsiveness as well as detection sensitivity are still left unsolved because a basic configuration of an optical system is exactly the same as in the case of the infrared absorption type concentration meter.
As described above, in case the conventional infrared absorption type or ultraviolet absorption type concentration meter is used, not only a problem of difficulties in downsizing and/or cost reduction of the equipment but many other problems that need to be fundamentally resolved quickly are left unsolved in responsiveness, detection sensitivity, detection precision, and reproducibility of the concentration measurement as well as in maintenance of airtightness and purity of the gas and so on.